CN1199053C - The method used to locate the location - Google Patents

Abstract

The invention relates to a method for locating a position. The method according to the invention comprises the following steps: receiving, at a server, satellite telemetry data for a plurality of satellites in a constellation; obtaining, at a server, an approximate location of a mobile device; deriving, at the server, a pseudorange model from the satellite telemetry data and the approximate position; propagating the pseudo-range model from the server to the mobile device; acquiring a plurality of satellite signals at the mobile device using the pseudorange model; and calculating a position of the mobile device using the plurality of satellite signals.

Description

The method used to locate the location

technical field

The present invention relates to signal processing in GPS receivers. In particular, the present invention relates to a method and apparatus for transmitting satellite data to a GPS receiver to enable the GPS receiver to acquire and lock to GPS satellite signals in low signal strength environments (eg, indoors).

Background technique

Conventional GPS receivers require an inordinate amount of time to acquire and lock onto satellite signals. Then, once locked, the GPS receiver extracts telemetry data (almanac and astronomical almanac) from this signal. From this data a GPS receiver can calculate information that can enhance its ability to lock on to satellite signals. A satellite signal of relatively high signal strength is necessary to enable the system to achieve an initial lock. Once a GPS signal is acquired, the signal strength must remain high while almanac and/or almanac data can be extracted from the satellite signal. Any severe attenuation of the signal will result in a loss of lock and the signal will need to be reacquired. Thus, the system has an inherent loop that makes it difficult or impossible for a GPS receiver to acquire a signal in low signal strength environments.

To aid in the initial acquisition of satellite signals, many GPS receivers store an almanac data from which the expected Doppler frequency of the satellite signal can be calculated. Some techniques have been developed to calculate useful information in a separate GPS receiver and then transmit this data to another GPS receiver. US Patent 6,064,336, issued May 16, 2000 collects almanac data from a single GPS receiver and then transmits the almanac data to a mobile receiver. The mobile receiver then uses this almanac data to calculate the expected Doppler frequency of the satellite signal, thereby aiding initial signal acquisition.

An advantage of receiving an almanac is that each GPS satellite repeatedly transmits a full almanac containing orbital information for the complete GPS constellation, so that a single GPS receiver tracking any satellite can collect and disseminate an almanac for all satellites in the constellation. The disadvantage of using this almanac is that it is a rather rough model of satellite orbit and satellite clock errors, so this almanac is only useful to reduce frequency uncertainty, but cannot be used to enhance receiver sensitivity by narrowing the search window where code delay uncertainty is not.

If a GPS receiver has a complete set of ephemeris data for all satellites in view before attempting to lock on to those satellites, the receiver will have significantly improved acquisition time and increased sensitivity. This is because this ephemeris data contains a precise description of satellite positions, velocities, and clock errors; and a GPS receiver can use this data to increase sensitivity by significantly reducing the search window for frequency uncertainty and code delay uncertainty. A disadvantage of the almanac is that each satellite transmits only its own almanac; therefore a single GPS receiver cannot collect and disseminate the almanac of all satellites in the constellation.

There is therefore a need for a technique for a GPS receiver system that can propagate satellite ephemeris for all satellites in the constellation, thereby enhancing the acquisition rate and signal sensitivity of mobile receivers.

Contents of the invention

In order to overcome the defects in the prior art, the invention discloses a method for locating a position. The method for locating a position according to the present invention comprises: receiving satellite telemetry data of a plurality of satellites in the constellation at the server; obtaining an approximate position of the mobile device at the server; deriving a pseudo-range model from the satellite telemetry data and the approximate position at the server; A pseudo-range model is propagated from a server to a mobile device; a plurality of satellite signals is acquired at the mobile device using the pseudo-range model; and a position of the mobile device is calculated using the plurality of satellite signals.

The present invention includes a method and apparatus for distributing and delivering Global Positioning System (GPS) satellite ephemeris using a communication link between a central location and a wide area network of GPS receivers. The wide area network of GPS receivers collects ephemeris data transmitted by satellites and relays the data to a central location. The central location transmits the almanac to the mobile receiver. The mobile GPS receiver utilizes the transmitted data to enhance its sensitivity in two ways. First, the data allows the receiver to detect very weak signals that the receiver would normally not be able to detect, and second, the GPS receiver does not have to track the satellite signal for long periods of time before it can calculate a position.

In one embodiment of the invention, the satellite ephemeris data is retransmitted without having to transform the data in any way. The GPS receiver can then use this data exactly as if the receiver had received the data from the satellite. In another embodiment, a satellite pseudo-range model is calculated from ephemeris data at a central location, and this pseudo-range model is transmitted to the GPS receiver. The pseudo-range model is characterized in that it is more compact than the full almanac. Thus, the GPS receiver does not have to perform as many calculations when using the pseudo-range model as when using the full ephemeris.

Description of drawings

The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:

Fig. 1 has described the structure of a kind of wide-area reference station network according to the present invention;

Fig. 2 has described a kind of GPS track sphere;

Figure 3 depicts the intersection of the GPS orbital sphere and the horizontal plane of the three reference stations;

Figures 4A and 4B depict the intersection of the GPS orbit sphere and the horizontal plane for four reference stations;

Figure 5 depicts a flowchart of a method of generating a pseudo-range model;

Figure 6 illustrates the time (pseudo-range) and frequency (pseudo-range rate) uncertainties of a mobile GPS receiver and the improvement in sensitivity obtained by reducing both uncertainties;

Figure 7 depicts a flowchart of a method of searching through time (pseudo-range) and frequency (pseudo-range rate) windows; and

FIG. 8 depicts a method of utilizing pseudorange information from satellites with high signal strengths to improve receiver sensitivity for signals received from satellites with low signal strengths.

Detailed ways

To facilitate understanding, the structure of this manual is as follows:

Summarizes , introduces each component of the present invention and describes their relationship to each other.

Global Tracking Network , describing how the worldwide network of tracking stations is constructed and configured to ensure that all satellites are tracked at all times.

Ephemeris Processing describes an embodiment of the present invention that provides a more compact and simpler model of satellite ephemeris.

Signal Detection , which describes how retransmitted satellite ephemeris data is used by GPS receivers to detect signals that would otherwise be undetectable.

Sensitivity Enhancement , which describes how the two strongest satellite signals are used to calculate time and correlator offsets at mobile receivers. This information is in turn used to increase the sensitivity of the mobile receiver to weaker GPS signals.

overview

Fig. 1 has described an embodiment of Global Positioning System (GPS) satellite data distribution system 100, comprises:

a) The reference station network 102 comprises a plurality of tracking stations 104 ₁ , 104 ₂ , . . . 104n connected to each other via a communication network 105 . Reference stations 104 are deployed over a wide area and include GPS receivers 126 so that ephemeris can be collected from all satellites 106 in a global network of satellites, such as the Global Positioning System (GPS). The ephemeris information consists of a 900-bit packet that includes satellite position and clock information.

b) The central processing location 108 that collects the almanac from the tracking station 104 includes an almanac processor 128 that removes repeated occurrences of the same almanac and provides the latest almanac data to the mobile GPS receivers 114 and 118 for reallocation.

c) Communication link 120 from central processing location to mobile GPS receiver 114 . The link 120 , which may be a landline 110 or other direct communication path, directly connects the mobile GPS receiver 114 to the central processing location 108 . Alternatively, the link has several parts, such as: land line 112 to wireless transmitter 116 and wireless link 122 from transmitter 116 to mobile receiver 118 .

d) Mobile GPS receiver 114 or 118, utilizing redistributed ephemeris data (or a modification thereof) to assist the receiver in detecting GPS signals from satellites 106 in the satellite constellation.

e) A position processor 130 which calculates the position of the GPS receiver 114 or 118 . This could be the GPS receiver itself, the central processing location 108 or some other location to which the mobile GPS receiver sends the measurements obtained from the satellites 106 .

In operation, each satellite 106 continuously broadcasts ephemeris information associated with that particular satellite. In order to fully and simultaneously capture ephemeris data for all satellites 106 in the constellation, the network 105 extends worldwide.

To obtain all ephemeris data, three or more tracking stations 104 are required. Each of the 28 satellites has an orbit inclined at 55 degrees relative to the Earth's equator. Thus, no satellite orbits beyond plus or minus 55 degrees of the orbiting sphere. Thus, three stations placed 120 degrees apart and exactly on the Earth's equator will see all satellites. However, it is impractical to place a base station at or near a precise location on or near the equator. In order to place reference stations in large cities around the world, the practical minimum number of all satellites 106 that can be seen is four.

Each tracking station 104 includes a GPS receiver 126 that acquires and tracks satellite signals from all satellites 106 in view. Station 104 extracts ephemeris information, which uniquely identifies each satellite's position, as well as satellite clock information, such as a 900-bit packet with a GPS signal. The ephemeris information is connected to a central processing location 108, for example via a landline network 105.

Central processing location 108 sends all or part of the ephemeris information to one or more mobile GPS receivers 114 and 118 . The central processing location 108 can only send satellite ephemeris information for what the mobile GPS receiver 114 or 118 is currently (or will be) seeing if the central processing location knows the approximate location of the mobile GPS receiver. The ephemeris information may be directly connected via landline 110 or other communication paths (eg, Internet, telephone, fiber optic cable, etc.). Alternatively, the ephemeris information may be connected to the mobile GPS receiver 118 via a wireless system 116, such as cellular telephone, wireless Internet, radio, television, or the like. The processing and utilization of ephemeris information is described below (see Ephemeris Processing and Signal Detection ).

Global Tracking Network

The global GPS reference network 102 has tracking stations 104 that are in view of all satellites at all times in the network 102 . Thus, the ephemeris of each satellite 106 is available to the network in real time, so the network can make the ephemeris or derived pseudorange models available to any mobile receivers that require them.

The smallest complete network of reference stations consists of three stations, roughly evenly placed on or near the Earth's equator. Figure 2 shows a GPS orbit sphere 202 around Earth 204, and a representation 206 of all orbits of the satellites. Figure 3 shows the intersection of the horizontal plane of the 3 tracking stations (denoted A, B and C) and the GPS orbit sphere. In Figure 3, any area on the orbital sphere at the level of a tracking station is colored gray. The area of the orbital sphere at the level of the two tracking stations is colored slightly darker. The orbital sphere is white above and below 55 degrees where there are no GPS satellites. From Figure 3, it is evident that any point on any GPS track is always at the level of at least one reference station A, B or C.

But it is not commercially or technically practical to place reference stations near the equator. A preferred location is a large city with a good communication infrastructure to enable the astronomical almanac to connect to the control processing location via a reliable network. When the reference station moves away from the equator, more than three stations are required to cover all satellites at all times. However, it is possible to create a network of as few as four base stations that provide full coverage of all GPS satellites at all times, where these four stations are located in or near large cities. For example, these stations may be placed in Honolulu, Hawaii (USA), Buenos Aires (Argentina), Tel Aviv (Israel), and Perth (Australia). Figures 4A and 4B show the intersection of the horizontal plane of these stations with the GPS orbit sphere. Any point on any GPS track is always on the level of at least one reference station. Figures 4A and 4B show the orbital sphere viewed from two points in space, one (Figure 4A) approximately in space on Spain and another (Figure 4B) on the opposite side of the sphere, approximately in New Zealand. This figure is colored in a similar manner to figure 3. Gray indicates the area of the GPS orbit sphere at the level of at least one tracking station, and dark gray areas indicate the portion of the orbit sphere reachable by both stations.

Almanac processing

The almanac model used to calculate satellite pseudoranges and pseudorange rates. From the pseudo-range rate, the mobile GPS receiver can calculate the Doppler shift for the satellite signal. Calculation of the pseudo-range model can be performed at the mobile receiver or at a central processing location. In a preferred embodiment, the pseudorange model is calculated at the center position as follows.

FIG. 5 depicts a flowchart of a method 500 for generating a pseudo-range model. In step 502, almanac data for all tracking stations is brought to a central processing location. Almanac data is transmitted continuously by all satellites, mostly repetitive data; a new almanac is usually transmitted every 2 hours. The ephemeris is marked with "time in ephemeris" denoted TOE. This mark indicates the time when the ephemeris is valid. Almanac calculations are very accurate within TOE 2 hours. A satellite first transmits the almanac 2 hours ahead of TOE, so any almanac is very accurate up to four hours.

In step 506, the central processing location holds all ephemeris data for the TOE closest to the time T at which the mobile receiver requires the ephemeris (or pseudo-range model). The time T is provided at step 504 by the mobile receiver. Usually T is the current actual time, but it can also be up to 4 hours in the future for mobile receivers that collect the almanac/pseudorange models before they are needed. T can also be a time in the past, used by the mobile receiver for processing previously stored data.

In step 508, the central processing position calculates the satellite position at time T. In the preferred embodiment, this is performed using the equations provided in the GPS Interface Control File, ICD-GPS-200-B.

In step 512, the central processing location obtains the approximate location of the mobile GPS receiver. In a preferred embodiment, the mobile GPS receiver communicates with the central processing location via a wireless communication link, such as a two-way paging network, or a mobile telephone network, or similar two-way wireless network. This two-way wireless network has communication towers that receive signals over an area of several miles. The central processing location obtains the reference ID of the wireless tower, which is used to receive the most recent communication from the mobile GPS. The central processing location then obtains the location of the wireless tower from a database. This location is used as an approximate mobile GPS location.

In an alternative embodiment, the approximate location of the mobile GPS receiver may simply be the center of an area served by the particular communications network used to implement the invention.

In another alternative embodiment, the approximate location of the mobile GPS receiver may be the last known point of said receiver, which is maintained in a centrally processed location database.

Of course many combinations and variations of the methods described above can be used to approximate the position of a mobile GPS receiver.

Having calculated the satellite positions and obtained the approximate user position, the central process calculates (at step 510) which satellites are or will soon be in the horizon of the mobile GPS receiver. For applications requiring only redistribution of ephemeris data, at step 514 the central processing location outputs the ephemeris for those satellites that are or will be on the horizon.

In a preferred embodiment, a pseudo-range model is calculated comprising: time T, and for each satellite that is or will be on the horizon: satellite PRN number, pseudo-range, pseudo-range velocity, and pseudo-range acceleration.

To calculate the pseudorange model, the central processing location first calculates at step 516 the pseudoranges of all satellites that are or will be on the horizon of the mobile GPS receiver. The pseudo-range is the geometric range between the satellite and the approximate GPS position, plus the satellite clock offset described by the almanac.

At step 518, pseudo-range rates may be calculated from satellite rates and clock drift. Satellite velocity can be obtained directly by differentiating the satellite position equation (in ICD-GPS-200-B) with respect to time. In an alternative embodiment, the satellite velocity may be calculated indirectly by calculating the satellite position at two different times, and then differencing the positions.

In another alternative embodiment, the pseudo-range rate may be calculated indirectly by computing the pseudo-ranges at two different times and then differentiating the pseudo-ranges.

In step 520, the pseudo-range acceleration is calculated in a similar manner (by differentiating the satellite velocity and clock drift with respect to time or by differencing the pseudo-range velocity).

The complete pseudorange model is then packed into a structure at step 522 and output to the mobile GPS receiver.

A mobile GPS receiver can use a pseudo-range model to derive the validity of its ephemeris. To apply the pseudo-range model at some time after time T, the mobile receiver propagates forward the pseudo-range and pseudo-range rate using the velocity and acceleration data contained in the pseudo-range model.

In an alternative embodiment, the ephemeris 519 where the position spread is unchanged is centrally processed and the pseudo-range model and pseudo-range rate are derived at the mobile GPS receiver.

Krasner (US Patent 6,064,336) has taught that Doppler information can be used to help mobile GPS receivers by reducing frequency uncertainty. US Patent 6,064,336 describes a system and method for transmitting almanac information from a mobile receiver from which the Doppler is derived; or equivalent information derived from the almanac; or Doppler measurements from a base station close to the mobile receiver itself. In another alternative embodiment of the invention, the ephemeris can be used to derive Doppler information. In the section after ( signal detection ), it is understood that this Doppler information will be used to help the signal capture to the pseudo-range rate uncertainty, that is, the degree to which the frequency bins to be searched are reduced, but the Doppler information Does not reduce the uncertainty (i.e. code latency) of pseudo-ranges.

Signal Detection

Ephemeris data (or derived pseudo-range models) can be used to aid signal acquisition and sensitivity of mobile GPS receivers in a number of ways, as described below.

An ephemeris or pseudo-range model predicts the satellite's elevation angle, allowing receivers to focus on capturing high-elevation satellite signals, which are generally less obstructed. Satellites that are calculated below the horizon (negative elevation) are ignored. This satellite selection can also be done using an almanac of satellite orbit information, but providing a model, or an almanac from which a model can be generated, eliminates the need for non-volatile storage of the almanac within the mobile receiver. Thus, almanac offers some advantages in this respect, but the main advantages of the present invention are improved signal acquisition and receiver sensitivity, as described below.

"Retransmitting" or "rebroadcasting" the ephemeris information improves the operation of the mobile receiver in two ways.

First, mobile receivers do not need to collect ephemeris from satellites. The almanac is broadcast from the satellite every 30 seconds and takes 18 seconds to transmit. In order to receive the almanac without utilizing the present invention, the mobile receiver requires clear, unobstructed satellite reception during the entire 18 second interval that the almanac is being transmitted. Depending on the environment and the use of the receiver, there may be several minutes before the situation permits the collection of the almanac. In many applications, such as indoor use, the mobile receiver never has an unobstructed view of the satellites. To eliminate data collection delays, the present invention provides almanac data directly to mobile receivers.

Second, as described above, the ephemeris is used to form a pseudorange model of the satellite signals received at the mobile receiver. These models can speed up the capture process in several ways.

The model predicts the pseudorange and pseudorange rate of the received signal. If the approximate user location is reasonably accurate, these models will estimate pseudo-range and pseudo-range rates very accurately. Using this model, the receiver can focus on the relevant processes around the desired signal.

Figure 6 shows a graph 601 of typical frequency and time uncertainties for a mobile GPS receiver. On the Y-axis 602, each row represents a different pseudo-range rate, and on the X-axis 604, each column represents a different pseudo-range. Without an accurate model, such as is available with the present invention, the range rate probabilities will vary considerably since wide range satellite operations are possible and the range probabilities will also vary over many cycles of the PN code. With an accurate model provided by the ephemeris information, the uncertainty can be reduced to a small area described by the black mesh 606 . Many receivers will be able to search this small area in a single process which eliminates the time consuming sequential retrieval and allows longer times to take advantage of better sensitivity, as will now be described.

Better sensitivity is achieved as follows: The sensitivity of a GPS receiver is a function of the amount of time the receiver can integrate the correlator output. The relationship between sensitivity and integration time is represented by graph 608 . If there are many bins to search, the integration time 610 is equal to the total available search time divided by the number of bins searched. If there is only a single bin to search, the integration time 612 is equal to the total available search time plus the sensitivity shown at 608 .

It should be noted that in some receivers the pseudo-range and pseudo-range rates that can be predicted from the pseudo-range model will not be accurate due to the lack of synchronization of the local clock. In this case, it is still initially necessary to search over a wide range of uncertainty, but only for the strongest satellites. If the local clock is known to be accurate to roughly one second of GPS time, then any one satellite is sufficient to synchronize the local correlator offsets. Thereafter, the desired pseudo-range and pseudo-range rate can be accurately calculated for the remaining satellites. If the local clock is not known to be within roughly one second, then two satellites must be used to calculate the two required clock parameters: local clock and correlator offset. The fact that two satellites are required is a point that is often misunderstood. In the GPS literature, it is often stated that one satellite is sufficient to solve for an unknown clock offset without having to implement it, and this is only true for systems where the local clock is already roughly synchronized to GPS time. In conventional GPS receivers that continuously track GPS signals, the local clock is synchronized to GPS time to a much better than one-second accuracy. In some more modern implementations (eg, US Patent 6,064,336), the local clock is synchronized to a network time reference, which is synchronized to GPS time. However, the present invention is specifically designed to operate in implementations where a local clock is not synchronized with GPS time. The way one solves for these clock parameters is described in detail below.

Once the unknown clock parameters have been calculated, the parameters can be used to adjust the pseudo-range model for the remaining, weaker satellites in order to narrow the uncertainty range to a narrower region; thus when high sensitivity is required, ie for Enhanced sensitivity accuracy when detecting weak satellite signals.

In other receivers, the local clock and clock rate can be quite precise. For example, if the clock signal is derived from a wireless medium (eg, a two-way paging network) that is time-synchronized with GPS, then the clock parameter is usually very accurate. In this case, there are no clock effects and a narrower search area can be used from the start.

To quantify the benefits of the present invention, consider an example where the user's location is known within the receiving radius (2 miles) of a two-way paging tower. In this case, the pseudo range (expressed in milliseconds) can be precomputed to hundredths of milliseconds accuracy. Without the present invention, the GPS receiver would search all possible code delays of one millisecond to lock onto the code transmitted by the satellite. With the present invention, the search window is reduced by a factor of one hundred, making the GPS receiver faster and, more importantly, allowing the use of longer integration times (as described above), enabling the receiver to detect weaker signals, such as occur in indoor.

An additional advantage of having an ephemeris or a derived pseudo-range model at a mobile receiver is that the process of identifying true correlations is more robust, because apart from increasing the integration time as mentioned above, if only correlations occurring within the desired range are considered, The chances of identifying a "false peak" are then greatly reduced.

One embodiment of enhancing sensitivity by using an ephemeris (or derived pseudorange model) is further described with reference to FIG. 7 .

FIG. 7 is a flowchart of a method 700 of signal searching. The method begins at step 702, where a pseudo-range model is input. As before, this pseudo-range model is calculated by the almanac, either in the mobile receiver itself or in a central processing location. At step 704, the model is applied at the mobile device's current time and used to estimate the expected current frequency and time of the GPS satellite signals, as well as the expected uncertainty of these quantities, to form frequency and code delay search windows for each satellite. This window is centered on the best estimates of frequency and delay, but allows for real deviations from the best estimates due to errors in the model building process, including inaccuracies in approximate user location, time of transmission from the wireless carrier, and frequency error and so on. Furthermore, the frequency uncertainty is divided into multiple frequency search bins to cover the frequency search window. As shown in Figure 6, the number of search boxes can be drastically reduced by using the pseudo-range model.

In step 706, the detection and measurement process is set to program the carrier correction to the first search frequency. At step 708, the code correlator is enabled to search for signal correlation within the delay range of the delay window. Such code correlators are standard technology, but the present invention drastically reduces the number of possible code delays that the correlator must search, thereby increasing the integration time per code delay, and receiver sensitivity.

At step 710, method 700 queries whether to detect a signal. If no signal is detected, then at step 712 the carrier correction is set to the next search frequency and the search continues until a signal is found or the frequency search bin is exhausted.

If at step 710, method 700 answers the query in the affirmative, then at step 714 this signal is used to further refine the estimates of clock time delay and clock frequency offset. This information is used at step 716 to recalculate the frequency and delay search windows for the remaining, undetected satellites. At step 718, the process continues until all satellites are detected or the search window has been exhausted.

The method of FIG. 7 illustrates one of various algorithms that can be used to guide the search process based on GPS signal processing capable of estimating time and frequency. Additionally, the algorithm can be changed to include various retry mechanisms, as the signals themselves may be attenuated or blocked.

Enhanced sensitivity

In order to enhance the sensitivity of the receiver (as described in Figure 6), the present invention utilizes the approximate location of the mobile device to calculate the desired pseudo-range, which reduces the pseudo-range uncertainty. However, before the receiver of the present invention can calculate the desired pseudo-range, the following three items are required:

1. Approximate location of mobile device (within miles of real location)

2. At the approximate time of the mobile device (within approximately one second of real time)

3. Correlator clock offset at mobile (within microseconds of true offset)

The more precisely each of these three terms is known, the more precisely the present invention constrains the pseudorange uncertainty, and therefore the greater the sensitivity (see Figure 6). In a preferred embodiment, the approximate location of the mobile device is determined from the known location of the last wireless tower used by the device. The reception radius of wireless towers for two-way pagers and cell phones is typically 3 kilometers. Therefore the approximate location of the mobile device is known to within 3 kilometers, and the error caused by the pseudo-range estimation does not exceed 3 kilometers. Referring to Figure 6, note that the total pseudo-range uncertainty for an unassisted GPS receiver is equal to one epoch, roughly 300 km. So even knowing an approximate location as rough as 3 kilometers can reduce the pseudo-range uncertainty by a factor of a hundred.

Timing errors can also cause errors in the desired pseudo-range. In order to calculate the desired pseudo-range, the receiver must calculate the satellite position in space. The range of a satellite at any location on Earth varies at a rate of plus or minus 800 m/s. So a time error per second will result in a range error (and pseudo-range error) of up to 800 meters.

This mobile device correlator delay offset leads to direct errors in pseudorange measurements, as is well known in the GPS literature. The unknown correlator delay offset per microsecond results in an error of 300 meters in the range measurement.

Therefore, in order to keep the pseudo-range estimate in the range of several kilometers (as shown in Fig. 6), the receiver of the present invention needs to estimate the position, time and correlator delay offset of the above range.

In an embodiment where the actual time of the mobile unit is not known for the better part of a few seconds and the correlator delay offset is not known, one solves for this using two satellite measurements as follows.

The equation that relates the pseudorange error to the two clock errors is:

y=c*dt _c -rangeRate*dt _s (1)

in:

y is the "pseudorange margin", i.e. the difference between the desired pseudorange and the measured pseudorange;

c is the speed of light;

dt _c , is the correlator delay offset; and

dt _s , is the offset from the actual time estimate.

FIG. 8 depicts a flowchart of a method 800 for improving clock parameters and then improving receiver sensitivity. Method 800 includes:

Step 802. Compute expected pseudo-ranges for all satellites using best known clock parameters.

Step 804. Measure the pseudoranges of the two strongest satellites with the highest signal strength.

Step 806. Using these two measurements, solve equation (1) for the two unknowns: dt _c and dt _s .

Step 808. Use dt _c and dt _s to refine the estimate of expected pseudo-range for the remaining (weaker) satellites.

Step 810. Use these improved desired pseudoranges to reduce pseudorange uncertainty, thus improving receiver sensitivity, as shown in FIG. 6 .

Although various embodiments that incorporate the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.

Claims (22)

1. method that is used for the position location comprises:

The satellite telemetering data of a plurality of satellites in server reception constellation;

Obtain the approximate location of mobile device at server;

Draw the pseudo-range model at server from satellite telemetering data and approximate location;

The pseudo-range model is propagated into mobile device from server;

Utilize this pseudo-range model to catch a plurality of satellite-signals at this mobile device; With

Utilize a plurality of satellite-signals to calculate the position of mobile device.

2. method as claimed in claim 1 is characterized in that the step of calculating location is carried out in mobile device.

3. method as claimed in claim 1 is characterized in that, also comprises:

Information in a plurality of satellite-signals is sent to server with the mobile device radio communication; With

In server, calculate the position of mobile device.

4. method as claimed in claim 1 is characterized in that server propagates into mobile device with the pseudo-range model by wireless communication system.

5. method as claimed in claim 4 is characterized in that, the step that obtains approximate location comprises:

Receive the position of the wireless towers of the used wireless communication system of mobile device and server communication period.

6. method as claimed in claim 3 is characterized in that, the step that obtains approximate location comprises:

Determine approximate location from the regional center of wireless communication system services.

7. method as claimed in claim 1 is characterized in that, the step that obtains approximate location comprises:

Safeguard the database of mobile device position; With

From database, receive the last known position of mobile device.

8. method as claimed in claim 1 is characterized in that satellite telemetering data comprises ephemeris data.

9. method as claimed in claim 1 is characterized in that, the pseudo-range model comprises pseudo-range, pseudo-range speed and pseudo-range acceleration.

10. method that is used for the position location comprises:

Reception is from the satellite telemetering data of a plurality of satellites in the stellar-based global-positioning system constellation;

The satellite telemetering data that receives is delivered to the center processing position;

Draw the pseudo-range model, this model comprises pseudo-range, pseudo-range speed and pseudo-range acceleration;

The pseudo-range model is propagated into mobile receiver; With

Utilize described pseudo-range model to catch at least one satellite-signal at described mobile receiver.

11. the method as claim 10 is characterized in that, the described step of catching also comprises from described pseudo-range Model Calculation Doppler.

12. the method as claim 10 is characterized in that, described satellite telemetering data comprises satellite clock signal and satellite position information.

13. the method as claim 10 is characterized in that, the pseudo-range model draws from satellite telemetering data, and this satellite telemetering data comprises the ephemeris data of each satellite that mobile receiver is seen.

14. the method as claim 13 is characterized in that, satellite telemetering data comprises the Doppler measurement value that draws from the satellite ephemeris data.

15. the method as claim 10 is characterized in that, the described step of catching further comprises:

Utilize the pseudo-range model that frequency uncertainty and code uncertainty are narrowed down.

16. the method as claim 10 is characterized in that, described receiving step utilizes four satellite signal receivers to realize.

17. the method as claim 10 is characterized in that, also comprises:

Utilize the position of the described mobile receiver of described pseudo-range Model Calculation.

18. the method as claim 17 is characterized in that, described calculation procedure is carried out in mobile receiver.

19. the method as claim 17 is characterized in that, described calculation procedure is carried out in the position away from described mobile receiver.

20. the method as claim 10 is characterized in that, described at least one satellite-signal is the signal with high signal intensity, and the described step of catching also comprises:

The satellite-signal that utilizes at least one to catch helps receive other satellite-signal with low signal intensity.

21. the method as claim 10 is characterized in that, described at least one satellite-signal of catching is used to generate clock and correlator postpones skew.

22. the method as claim 10 is characterized in that, the estimation pseudo-range that described at least one satellite-signal of catching is used to improve for the satellite-signal with low signal intensity calculates.

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